Imaging system, processing device and illumination control method

ABSTRACT

An imaging system includes: a light source configured to emit illumination light; an imager configured to store an electric charge corresponding to an amount of received light and read out the stored electric charge as a signal value by using a rolling shutter method; a frequency detector configured to detect a vibrational frequency of a predetermined site of a subject; and an illumination controller configured to control emission of the illumination light during a readout period of the signal value. The illumination controller is configured to set a phrase for an emission timing of the illumination light in an exposure period during which the imager stores the electric charge to be an identical phase at the frequency in each frame, and refer to respective phases set in exposure periods of chronologically adjacent frames to set an emission timing of the illumination light in the readout period.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of PCT International Application No.PCT/JP2019/002378 filed on Jan. 24, 2019, which designates the UnitedStates, incorporated herein by reference, and which claims the benefitof priority from Japanese Patent Application No. 2018-021867, filed onFeb. 9, 2018, incorporated herein by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to an imaging system including a lightsource that emits illumination light and an imaging element, aprocessing device, and an illumination control method.

2. Related Art

In medical fields, an endoscope system is conventionally used to observethe inside of the body of a subject. In an endoscope system, generally,a flexible insertion portion having an elongated shape is inserted intothe body of the subject such as a patient, illumination light is emittedfrom the distal end of the insertion portion, and the reflected light ofthe illumination light is received by an imaging unit at the distal endof the insertion portion to capture the in-vivo image. The thus capturedbiological image is presented on a display of the endoscope system.

When the observation target is vocal cords so as to observe thevocal-cord motion during voice production, the vocal cords areintermittently illuminated with strobe light, and the image of the vocalcords is captured (for example, see Japanese Laid-open PatentPublication No. 2002-172088). FIGS. 7 and 8 are graphs illustrating theemission timings in a conventional endoscope system. In the case ofimaging with strobe light, the light is emitted at different phases(phases P_(E) 101, P_(E) 102, P_(E) 103, . . . , P_(E) 108, . . . )shifted from the vocal-cord frequency (see FIG. 7). Here, the vocalcords are illuminated multiple number of times at different phases in atime period (e.g., frame periods F101 and F102) corresponding to oneframe. In Japanese Laid-open Patent Publication No. 2002-172088, inorder to suppress the blurring of an image due to multiple lightemissions in one frame, the emission timings in the identical frame areset to be emitted at identical phases (phases P_(E) 111, P_(E) 112,P_(E) 113, . . . ) (see FIG. 8).

SUMMARY

In some embodiments, an imaging system includes: a light sourceconfigured to emit illumination light; an imager configured to store anelectric charge corresponding to an amount of received light and readout the stored electric charge as a signal value by using a rollingshutter method; a frequency detector configured to detect a vibrationalfrequency of a predetermined site of a subject; and an illuminationcontroller configured to control emission of the illumination lightduring a readout period of the signal value. The illumination controlleris configured to set a phrase for an emission timing of the illuminationlight in an exposure period during which the imager stores the electriccharge to be an identical phase at the frequency in each frame, andrefer to respective phases set in exposure periods of chronologicallyadjacent frames to set an emission timing of the illumination light inthe readout period.

In some embodiments, provided is a processing device configured to beconnected to an endoscope including an imager configured to read out anelectric charge stored in a pixel by using a rolling shutter method. Theprocessing device includes: a frequency detector configured to detect afrequency of a predetermined site of a subject; and an illuminationcontroller configured to control emission of the illumination lightduring a readout period of the signal value. The illumination controlleris configured to set a phrase for an emission timing of the illuminationlight in an exposure period during which the imager stores the electriccharge to be an identical phase at the frequency in each exposureperiod, and refer to respective phases set in exposure periods ofchronologically adjacent frames to set an emission timing of theillumination light in the readout period.

In some embodiments, provided is an illumination control methodimplemented by an imaging system including: a light source configured toemit illumination light; and an imager configured to store an electriccharge corresponding to an amount of received light and read out thestored electric charge as a signal value by using a rolling shuttermethod. The illumination control method includes: detecting avibrational frequency of a predetermined site of a subject; setting aphrase for an emission timing of the illumination light in an exposureperiod during which the imager stores the electric charge to be anidentical phase at the frequency in each frame; and referring torespective phases set in exposure periods of chronologically adjacentframes to set an emission timing of the illumination light in a readoutperiod of the signal value.

The above and other features, advantages and technical and industrialsignificance of this disclosure will be better understood by reading thefollowing detailed description of presently preferred embodiments of thedisclosure, when considered in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a schematic configuration of anendoscope system according to a first embodiment of the disclosure;

FIG. 2 is a block diagram illustrating a schematic configuration of theendoscope system according to the first embodiment of the disclosure;

FIG. 3 is a graph illustrating a strobe emission process performed by anillumination controller of the endoscope system according to the firstembodiment of the disclosure;

FIG. 4 is a graph illustrating a strobe emission process performed by anillumination controller of the endoscope system according to the firstembodiment of the disclosure;

FIG. 5 is a graph illustrating a strobe emission process performed bythe illumination controller of the endoscope system according to asecond embodiment of the disclosure;

FIG. 6 is a graph illustrating a strobe emission process performed bythe illumination controller of the endoscope system according to amodification of the second embodiment of the disclosure;

FIG. 7 is a graph illustrating emission timings in a conventionalendoscope system; and

FIG. 8 is a graph illustrating emission timings in a conventionalendoscope system.

DETAILED DESCRIPTION

Modes (hereinafter referred to as “embodiments”) for carrying out thedisclosure are described below. In the embodiments, a medical endoscopesystem that captures and displays an image inside the body cavity of asubject, such as a patient, is described as an example of an imagingsystem according to the disclosure. The disclosure is not limited to theembodiments. In the description of the drawings, the same components aredenoted by the same reference numeral.

First Embodiment

FIG. 1 is a schematic view illustrating a schematic configuration of anendoscope system according to a first embodiment of the disclosure. Asillustrated in FIG. 1, an endoscope system 1 according to the firstembodiment includes: an endoscope 2 (scope) that is introduced into thebody of the subject to capture the image inside the body of the subjectand generate the image signal of the inside of the subject's body; avoice input device 3 that receives a voice; a processing device 4 thatperforms predetermined image processing on the imaging signal capturedby the endoscope 2 and controls each unit of the endoscope system 1; alight source device 5 (light source unit) that generates pulsed light asillumination light (observation light) of the endoscope 2; and a displaydevice 6 that displays the image corresponding to the image signalgenerated by the processing device 4 after image processing.

The endoscope 2 includes: an insertion portion 21 that is inserted intothe subject; an operating unit 22 that is provided on the proximal endside of the insertion portion 21 so as to be grasped by the operator;and a flexible universal cord 23 that extends from the operating unit22.

The insertion portion 21 is implemented by using an illumination fiber(light guide cable), an electric cable, etc. The insertion portion 21includes: a distal end portion 211 including an imaging unit having abuilt-in imaging element that captures the inside of the subject; abendable curved portion 212 including a plurality of bendable pieces;and a flexible tube portion 213 having flexibility and provided on theproximal end side of the curved portion 212. The distal end portion 211includes an illumination unit that illuminates the inside of the subjectvia an illumination lens; an observation unit that captures the insideof the subject; an opening that communicates with a treatment toolchannel; and an air/water supply nozzle (not illustrated).

The operating unit 22 includes: a curving knob 221 that curves thecurved portion 212 in a vertical direction and a horizontal direction; atreatment tool insertion portion 222 through which a treatment tool,such as biopsy forceps or a laser scalpel, is inserted into the bodycavity of the subject; and a plurality of switch portions 223 thatoperate peripheral devices such as the processing device 4, the lightsource device 5, an air supply device, a water supply device, or a gassupply device. A treatment tool inserted through the treatment toolinsertion portion 222 is exposed from an opening at the distal end ofthe insertion portion 21 via the treatment tool channel provided inside.

The universal cord 23 is configured by using an illumination fiber, anelectric cable, etc. The universal cord 23 branches at the proximal endthereof so that the end of a branch cord 231, which is one of thebranches, is a connector 232 and the proximal end of the other one is aconnector 233. The connector 232 is attachable to and detachable fromthe processing device 4, and the connector 233 is attachable to anddetachable from the light source device 5. The universal cord 23propagates the illumination light emitted from the light source device 5to the distal end portion 211 via the connector 232, the operating unit22, and the flexible tube portion 213. The universal cord 23 transmitsthe imaging signal captured by the imaging unit provided in the distalend portion 211 to the processing device 4.

An illumination fiber 214 (see FIG. 2) that guides illumination lightfrom the light source device 5 is disposed in the insertion portion 21and the universal cord 23. One end of the illumination fiber 214 islocated at the distal end surface of the insertion portion 21, and theother end thereof is located at the connection surface between theuniversal cord 23 and the light source device 5.

The voice input device 3 receives the input of a voice generated byvocal cords when the object of capturing is the vocal cords. The distalend of a cord 31 is coupled to the voice input device 3, and a connector311 at the proximal end is attachable to and detachable from theprocessing device 4. The voice input device 3 outputs the input voice tothe processing device 4 via the cord 31 and the connector 311. The voiceinput device 3 corresponds to a vocal-cord vibration input unit.

The processing device 4 performs predetermined image processing on theimaging signal on the inside of the subject's body captured by theimaging unit in the distal end portion 211 of the endoscope 2 and inputvia the universal cord 23. The processing device 4 controls each unit ofthe endoscope system 1 based on various instruction signals transmittedfrom the switch portion 223 in the operating unit 22 of the endoscope 2via the universal cord 23.

The light source device 5 is configured by using a light source thatemits pulsed white light as illumination light (hereinafter referred toas pulsed light), a condenser lens, etc. The light source device 5receives a light control signal from the processing device 4 andperforms PWM (Pulse Width Modulation) control on the driving timing(light emission period) for driving the light source based on the lightcontrol signal. Accordingly, the light source device 5 emits pulsedlight by pulse driving under the control of an illumination controller408. The light source device 5 feeds the pulsed light from the lightsource to the endoscope 2 coupled thereto via the connector 232 and theuniversal cord 23 (the illumination fiber) as illumination light forilluminating (intermittently illuminating) the inside of the subject'sbody that is the object of capturing.

The display device 6 is configured by using a display, or the like,using a liquid crystal or an organic EL (Electro Luminescence). Thedisplay device 6 presents various types of information including theimage corresponding to the display image signal generated by theprocessing device 4 via a video cable 61. This allows the operator toobserve the desired position inside the subject and determine theproperties while viewing the image (in-vivo image) presented by thedisplay device 6 and operating the endoscope 2.

Next, configurations of the endoscope 2, the voice input device 3, theprocessing device 4, and the light source device 5 illustrated in FIG. 1are described. FIG. 2 is a block diagram schematically illustrating aconfiguration of the endoscope system 1.

The endoscope 2 includes an imaging unit 24 at the distal end portion211. The imaging unit 24 includes: an optical system 241 such as anobjective lens disposed on the light receiving surface side of a lightreceiving unit 242 a which is described later; and an imaging element242 that is provided at the imaging position of the optical system 241to receive the light condensed by the optical system 241 and executephotoelectric conversion to obtain an electric signal.

The imaging element 242 is implemented by using a CMOS (ComplementaryMetal Oxide Semiconductor) image sensor. The imaging element 242includes the light receiving unit 242 a and a readout unit 242 b.

The light receiving unit 242 a receives, with the light receivingsurface, the light from the object illuminated with the pulsed lightfrom the light source device 5 and executes the photoelectric conversionon the received light to generate an electric signal. Specifically, thelight receiving unit 242 a includes a plurality of pixels arranged in amatrix and each having, for example, a photodiode that stores theelectric charge corresponding to the amount of light and a capacitorthat converts the electric charge transferred from the photodiode into avoltage level (signal value), and each of the pixels executes thephotoelectric conversion on the light from the optical system 241 togenerate an electric signal. In the light receiving unit 242 a, two ormore pixels are arranged in a pixel row (horizontal line) in ahorizontal direction, and the pixel rows are arranged in a verticaldirection.

The readout unit 242 b sequentially reads the electric signal (signalvalue) generated by any pixel that is set as the readout target amongthe pixels of the light receiving unit 242 a and outputs the electricsignal as an imaging signal. The readout unit 242 b executes theexposure on the pixels in the light receiving unit 242 a and the readoutof electric signals from the pixels. The readout unit 242 b sequentiallyreads the electric signal generated by each of the pixels arranged in amatrix in each horizontal line (pixel row). The readout unit 242 bgenerates an imaging signal by using a rolling shutter method, that is,performs the imaging operation including the exposure and the readout,starting from the horizontal line at the beginning, shifts the timing ineach horizontal line, and executes the electric charge reset (the resetof the capacitor), the exposure, and the readout.

Thus, in the imaging unit 24, the exposure timing and the readout timingare different in each horizontal line even during one imaging period(frame). The readout unit 242 b outputs the electric signal (imagingsignal) read from the pixels of the light receiving unit 242 a to theprocessing device 4 via a cable (not illustrated) and the connector 232.

Next, the processing device 4 is described. The processing device 4includes an AGC (Auto Gain Control) 401, a strobe processing unit 402,an image processing unit 403, a memory 404, a display controller 405, aninput unit 406, a vocal-cord frequency detecting unit 407, theillumination controller 408, and a control unit 409. According to thepresent embodiment, the processing device 4, the endoscope 2, and thelight source device 5 operate in accordance with a clock signalgenerated by a clock generator (not illustrated) provided in theprocessing device 4.

The AGC 401 adjusts the amplification factor (gain) of an electricsignal to maintain a constant output level. The AGC 401 is configured byusing a general-purpose processor such as a CPU (Central ProcessingUnit) or a dedicated processor such as various arithmetic circuitriesthat execute a specific function, e.g., an ASIC (Application SpecificIntegrated Circuit) or an FPGA (Field Programmable Gate Array) that is aprogrammable logic device capable of rewriting the processing contents.

The strobe processing unit 402 acquires a PWM signal for controlling theintermittent illumination with pulsed light from the light source device5 and outputs an imaging signal input from the AGC 401 in associationwith the PWM signal to the image processing unit 403. The strobeprocessing unit 402 is configured by using a general-purpose processorsuch as a CPU or a dedicated processor such as various arithmeticcircuitries that execute a specific function, e.g., an ASIC or an FPGA.

The image processing unit 403 executes predetermined signal processingon the electric signals (imaging signals) of the pixels read by thereadout unit 242 b of the imaging unit 24 to generate image signals. Forexample, the image processing unit 403 performs, on an imaging signal,image processing including at least an optical black subtractionprocess, a white balance (WB) adjustment process, a synchronizationprocess in the case of an imaging element having the Bayer arrangement,a color matrix calculation process, a gamma correction process, a colorreproduction process, an edge enhancement process, and the like. Theimage processing unit 403 is configured by using a general-purposeprocessor such as a CPU or a dedicated processor such as variousarithmetic circuitries that execute a specific function, e.g., an ASICor an FPGA.

The memory 404 stores various programs for operating the processingdevice 4 and the light source device 5. The memory 404 temporarilystores the information that is being processed by the processing device4. The memory 404 stores the imaging signals, read by the readout unit242 b, corresponding to the matrix arrangement of the pixels in thelight receiving unit 242 a in units of frame. The memory 404 stores theimage signals generated by the image processing unit 403 in units offrame. The memory 404 is configured by using a RAM (Random AccessMemory), a ROM (Read Only Memory), and the like. The memory 404 may beconfigured by using a memory card, or the like, attached at the outsideof the processing device 4.

The display controller 405 selects a display image signal from the imagesignals of frames generated by the image processing unit 403 inaccordance with the display cycle of the display device 6 and outputsthe selected image signal as the image signal to be displayed on thedisplay device 6. Alternatively, the display controller 405 combines theimage signals of frames generated by the image processing unit 403 foreach display period of the display device 6 to generate a display imagesignal and outputs it to the display device 6. The display controller405 converts the display image signal from a digital signal into ananalog signal, changes the format of the analog image signal after theconversion into a format such as a high-definition format, and outputsit to the display device 6. The display controller 405 is configured byusing a general-purpose processor such as a CPU or a dedicated processorsuch as various arithmetic circuitries that execute a specific function,e.g., an ASIC or an FPGA.

The input unit 406 is implemented by using an operating device such as amouse, a keyboard, or a touch panel to receive the input of varioustypes of instruction information (instruction signals) of the endoscopesystem 1. Specifically, the input unit 406 receives the input of varioustypes of instruction information such as subject information (e.g., theID, the date of birth, or the name), the identification information(e.g., the ID or examination corresponding item) on the endoscope 2, orexamination content.

The vocal-cord frequency detecting unit 407 detects the frequency(vocal-cord frequency) of the voice (the vibration of vocal cords) inputto the voice input device 3 and input to the processing device 4 via thecord 31 and the connector 311. According to the first embodiment, thevoice is generated from the vocal cords of the subject. The vocal-cordfrequency detecting unit 407 outputs the detected frequency of the voiceto the control unit 409. The vocal-cord frequency detecting unit 407 isconfigured by using a general-purpose processor such as a CPU or adedicated processor such as various arithmetic circuitries that executea specific function, e.g., an ASIC or an FPGA.

The illumination controller 408 controls the operation of the lightsource device 5. Specifically, the illumination controller 408 controlsthe emission timing and the illumination period of pulsed light from alight source 51 in synchronization with the frequency of the voicedetected by the vocal-cord frequency detecting unit 407. Theillumination controller 408 generates the pulse for driving the lightsource 51 based on the vocal-cord frequency detected by the vocal-cordfrequency detecting unit 407 and the preset light emission period (thepulse width or the duty ratio), generates the light-source control PWMsignal including the pulse, and outputs it to a pulse generating unit53. The illumination controller 408 outputs the generated PWM signal tothe control unit 409. The illumination controller 408 is configured byusing a general-purpose processor such as a CPU or a dedicated processorsuch as various arithmetic circuitries that execute a specific function,e.g., as an ASIC or an FPGA.

The illumination controller 408 includes a phase setting unit 408 a. Thephase setting unit 408 a sets the phase for emitting the strobe lightwith regard to the vocal-cord vibration (vocal-cord frequency). Thephase setting of the strobe emission by the phase setting unit 408 a isdescribed later.

The control unit 409 controls the processing operation of each unit ofthe processing device 4. The control unit 409 executes, for example, thetransfer of instruction information and data to each component of theprocessing device 4 so as to control the operation of the processingdevice 4. The control unit 409 is coupled to the imaging unit 24 and thelight source device 5 via each cable. The control unit 409 also controlsthe operation of the imaging unit 24. In the description according tothe present embodiment, the imaging element 242 and the light source 51are driven at the synchronized imaging timing and illumination timingunder the control of the control unit 409. The control unit 409 isconfigured by using a general-purpose processor such as a CPU or adedicated processor such as various arithmetic circuitries that executea specific function, e.g., an ASIC or an FPGA.

Next, the light source device 5 is described. The light source device 5includes the light source 51, a light source driver 52, and a pulsegenerating unit 53.

The light source 51 is configured by using a light source such as awhite LED that emits pulsed white light (pulsed light) and an opticalsystem such as a condenser lens. The light source 51 generates theillumination light to be supplied to the endoscope 2 and guides theillumination light to the endoscope 2 via an illumination fiber, etc.

The light source driver 52 supplies a predetermined electric power tothe light source 51 based on the PWM signal generated by the pulsegenerating unit 53. Accordingly, the subject is illuminated with thelight (pulsed light) that is emitted from the light source 51 throughthe distal end portion 211 of the insertion portion 21 via the connector233 and the universal cord 23.

The pulse generating unit 53 generates the pulse for driving the lightsource 51 based on the PWM signal acquired from the illuminationcontroller 408, generates the light source control signal including thepulse, and outputs it to the light source driver 52.

Next, the phase setting of the strobe emission by the phase setting unit408 a is described with reference to FIGS. 3 and 4. FIGS. 3 and 4 aregraphs illustrating the strobe emission process performed by theillumination controller of the endoscope system according to the firstembodiment of the disclosure. In the case of the imaging with the strobeemission, the emission is executed while the phase is shifted in thevocal-cord frequency. The phase setting unit 408 a sets the phases(phases P_(PE) 1, P_(PE) 2, P_(PE) 3, . . . , P_(PE) 16, . . . ) oftemporary emission timings with regard to the vocal-cord vibration(vocal-cord frequency) illustrated in FIG. 3. During the strobe emissionexecuted at the temporary emission timings, the illumination light isintermittently emitted while the phase is slightly shifted in one cycleas described above. For this reason, in each frame (frames F1, F2, F3,F4, . . . ), the illumination light is emitted multiple number of timesto the vocal cord in different phases, that is, in different openstates. The term “frame” here corresponds to a time period during whichall the pixels are exposed and the time period during which one image isdisplayed on the display device 6.

The phase setting unit 408 a refers to the readout timing of the readoutunit 242 b to set the readout period and the full exposure period of theimaging operation performed by the imaging unit 24. For example, asillustrated in FIG. 3, the phase setting unit 408 a sets total readoutperiods T_(F) 1, T_(R) 2, T_(R) 3, . . . , from the line (a line 1) forstarting the readout to the last line (a line N: N is a natural numberequal to or more than two). Then, the phase setting unit 408 a sets fullexposure periods T_(E) 1, T_(E) 2, T_(E) 3, T_(E) 4, . . . , which areprovided between the chronologically adjacent total readout periods andduring which all the pixels store the electric charge. The full exposureperiods T_(E) 1, T_(E) 2, T_(E) 3, T_(E) 4, . . . , are synchronizedwith the frames (video frames) F1, F2, F3, F4, . . . , respectively,each frame being for displaying one image.

Then, with regard to the full exposure periods T_(E) 1, T_(E) 2, T_(E)3, T_(E) 4, . . . , the phase setting unit 408 a sets a phase for thestrobe emission in each full exposure period. According to the firstembodiment, the phase setting unit 408 a sets a first phase in each fullexposure period as each of emission phases (phases for the strobeemission) in the full exposure period. As illustrated in for exampleFIG. 4, the phase setting unit 408 a sets the emission timings in thefull exposure period T_(E) 1 to be emitted at the identical phases.During the full exposure period T_(E) 1, each of the phases at thetemporary emission timings is set to be a phase P_(E) 1 that isidentical to the phase P_(PE) 1 at the first emission timing.Specifically, during the full exposure period T_(E) 1, each of thephases P_(PE) 2 and P_(PE) 3 illustrated in FIG. 3 is changed to thephase P_(E) 1 that is identical to the phase P_(PE) 1. Similarly, thephase setting unit 408 a sets the phases P_(E) 2, P_(E) 3, P_(E) 4, . .. , which are identical to the phases P_(PE) 5, P_(PE) 9, and P_(PE) 14,. . . , respectively, as each of phases for the strobe emission in eachof the full exposure periods T_(E) 2, T_(E) 3, T_(E) 4, . . . . Due tothe phase setting described above, the subject's vocal cords having theidentical open state are illuminated in each frame. Thus, the imageacquired during the full exposure period is the vocal-cord image havingless blurring or unevenness in brightness. In the example describedaccording to the first embodiment, the phase at the first emissiontiming in each of the full exposure periods is set as each of the phasesfor the strobe emission in the full exposure period; however, theaverage value of phases at the emission timings included in the fullexposure period may be set as each of the phases for the strobe emissionin the full exposure period.

After setting the phases of the full exposure periods T_(E) 1, T_(E) 2,T_(E) 3, T_(E) 4, . . . , the phase setting unit 408 a sets the phasefor the emission in each of the total readout periods T_(R) 1, T_(R) 2,T_(R) 3, . . . . The phase setting unit 408 a calculates the average ofthe phases set in the frames previous to and subsequent to the readoutperiod and sets the averaged phase as the emission phase in the totalreadout period.

As illustrated in for example FIG. 4, with regard to the total readoutperiod T_(R) 1, the phase setting unit 408 a calculates the averagevalue of the phase P_(E1) set in the frame F1 and the phase P_(E) 2 setin the frame F2 and sets the averaged phase (a phase P_(E) 11) as thephase for the strobe emission. Similarly, with regard to the totalreadout periods T_(R) 2, T_(R) 3, . . . , the phase setting unit 408 asets the phases (phases P_(E) 12, P_(E) 13, . . . ), which are theaverage of the phases in the adjacent frames, as the phase for thestrobe emission. As the exposure processes for two frames are mixedduring the readout period, the emission at the intermediate phasebetween the phases in the two frames enables the averaging of blurringthat occurs in the frames.

The illumination controller 408 generates a PWM signal based on thephase set by the phase setting unit 408 a. The pulse generating unit 53generates a pulse based on the acquired PWM signal so as to drive thelight source driver 52 and cause the light source 51 to emit the strobe.All of the strobe emissions have the same emission intensity. Theemission intensities in the full exposure period and the total readoutperiod may be set to be different from each other.

According to the first embodiment described above, with regard to thefull exposure periods T_(E) 1, T_(E) 2, T_(E) 3, T_(E) 4, . . . , eachof the phases for the strobe emission in the frame is set to be theidentical phase and, with regard to the total readout periods T_(F) 1,T_(R) 2, T_(R) 3, . . . , the average of the phases set in the adjacentframes is calculated and the averaged phase is set as the emission phasein the total readout period. According to the first embodiment, even inthe case of sequential imaging using the rolling shutter method, it ispossible to suppress blurring of a vocal-cord image.

Second Embodiment

Next, a second embodiment of the disclosure is described. An endoscopesystem according to the second embodiment has the same configuration asthat of the above-described endoscope system 1. The second embodiment isdifferent from the first embodiment described above in the phase settingduring the readout period. A setting process, which is different fromthat in the first embodiment described above, is described withreference to FIG. 5. FIG. 5 is a graph illustrating a strobe emissionprocess performed by the illumination controller of the endoscope systemaccording to the second embodiment of the disclosure.

The phase setting unit 408 a sets a phase for the strobe emission ineach of the full exposure periods T_(E) 1, T_(E) 2, T_(E) 3, T_(E) 4, .. . , in the same manner as in the first embodiment. Specifically, thephase setting unit 408 a sets a first phase in each full exposure periodas each of emission phases in the full exposure period. As illustratedin for example FIG. 5, the phase setting unit 408 a sets phases for thestrobe emission in the full exposure periods T_(E) 1, T_(E) 2, T_(E) 3,T_(E) 4, . . . to be the phases P_(E) 1, P_(E) 2, P_(E) 3, P_(E) 4, . .. , respectively.

After setting the phases in the full exposure periods T_(E) 1, T_(E) 2,T_(E) 3, T_(E) 4, . . . , the phase setting unit 408 a sets therespective phases for the emission in the total readout periods T_(R) 1,T_(R) 2, T_(R) 3, . . . . According to the second embodiment, the phasesetting unit 408 a sets the phase in the chronologically previous frameout of the phases set in the frames previous to and subsequent to thereadout period as the emission phase in the total readout period. Asillustrated in for example FIG. 5, with regard to the total readoutperiod T_(R) 1, the phase setting unit 408 a sets the phase (a phaseP_(E) 21) identical to the phase P_(E) 1 set in the frame F1 as thephase for the strobe emission. Similarly, with regard to the totalreadout periods T_(R) 2, T_(R) 3, . . . , the phase setting unit 408 asets the phases (phases P_(E) 22, P_(E) 23, . . . ) identical to thephases P_(E) 2, P_(E) 3, . . . in the frame before the readout period asthe phase for the strobe emission, respectively.

The illumination controller 408 generates a PWM signal based on thephase set by the phase setting unit 408 a. The pulse generating unit 53generates a pulse based on the acquired PWM signal so as to drive thelight source driver 52 and cause the light source 51 to emit the strobe.According to the second embodiment, the emission intensity in the totalreadout period is set to be lower than the emission intensity in thefull exposure period.

According to the second embodiment described above, with regard to thefull exposure period, each of the phases for the strobe emission in theframe is set to be the identical phase, with regard to the total readoutperiod, the phase set in the frame before the total readout period isset as the emission phase in the total readout period, and the emissionintensity in the total readout period is set to be lower than theemission intensity in the full exposure period. Thus, even though thephase in the frame after the readout period is different from the phasein the full exposure period, the effect of blurring of a vocal-cordimage due to the exposure in the total readout period may be reduced.According to the second embodiment, even in the case of sequentialimaging using the rolling shutter method, it is possible to suppress theblurring of a vocal-cord image.

Modification of the Second Embodiment

Next, a modification of the second embodiment of the disclosure isdescribed. An endoscope system according to the present modification hasthe configuration similar to that of the above-described endoscopesystem 1. The present modification is different from the above-describedsecond embodiment in the phase setting during the readout period. Asetting process different from that in the above-described secondembodiment is described below with reference to FIG. 6. FIG. 6 is agraph illustrating a strobe emission process performed by theillumination controller of the endoscope system according to themodification of the second embodiment of the disclosure.

The phase setting unit 408 a sets a phase for the strobe emission ineach of the full exposure periods T_(E) 1, T_(E) 2, T_(E) 3, T_(E) 4, .. . , in the same manner as in the first embodiment and the secondembodiment. Specifically, the phase setting unit 408 a sets a firstphase in each full exposure period as each of emission phases in thefull exposure period.

After setting the phases in the full exposure periods T_(E) 1, T_(E) 2,T_(E) 3, T_(E) 4, . . . , the phase setting unit 408 a sets the phasefor the emission in each of the total readout periods T_(R) 1, T_(R) 2,T_(R) 3, . . . . According to the present modification, the phasesetting unit 408 a sets the phase in the chronologically subsequentframe out of the phases set in the frames previous to and subsequent tothe readout period as the emission phase in the total readout period. Asillustrated in for example FIG. 6, with regard to the total readoutperiod T_(R) 1, the phase setting unit 408 a sets the phase (a phaseP_(E) 31) identical to the phase P_(E) 2 set in the frame F2 as thephase for the strobe emission. Similarly, with regard to the totalreadout periods T_(R) 2, T_(R) 3, . . . , the phase setting unit 408 asets the phases (phases P_(E) 32, P_(E) 33, . . . ) identical to thephases P_(E) 3, P_(E) 4, . . . in the frame after the readout period asthe phase for the strobe emission, respectively.

The illumination controller 408 generates a PWM signal based on thephase set by the phase setting unit 408 a. The pulse generating unit 53generates a pulse based on the acquired PWM signal so as to drive thelight source driver 52 and cause the light source 51 to emit the strobe.According to the present modification, the emission intensity in thetotal readout period is set to a value lower than the emission intensityin the full exposure period.

According to the modification described above, with regard to the fullexposure period, each of the phases for the strobe emission in the frameis set to be the identical phase, with regard to the total readoutperiod, the phase set in the frame after the total readout period is setas the emission phase in the total readout period, and the emissionintensity in the total readout period is set to be a value lower thanthe emission intensity in the full exposure period. Thus, even thoughthe phase in the frame before the readout period is different from thephase in the full exposure period, the effect of blurring of avocal-cord image due to the exposure in the total readout period may bereduced. According to the present modification, even in the case ofsequential imaging using the rolling shutter method, it is possible tosuppress the blurring of a vocal-cord image.

In addition to the phase setting example according to theabove-described modification, the average of the phases in the adjacentframes as described above in the first embodiment may be set as thephase in the total readout period, or the conventionally set phaseillustrated in FIG. 3, e.g., the intermediate phase between the phasesset in the full exposure periods of the adjacent frames may be set asthe phase in the total readout period.

In the first embodiment and the second embodiment described above, it ispossible to provide a rotary filter including a plurality of filtersthat is arranged on the optical path of white light (illumination light)emitted from the light source 51 to rotate so as to exclusively allowthe passage of light having a predetermined wavelength band included inthe white light. The provided rotary filter allows the light having anindividual wavelength band, such as red light (R), green light (G), andblue light (B), to be sequentially transmitted and emitted. Bycontrolling the rotation of the rotary filter in accordance with theemission timing of pulsed light, any of red light (R illumination),green light (G illumination), and blue light (B illumination) having anarrow band, included in the white light emitted from the light source51, may be sequentially emitted to the endoscope 2 (sequentiallighting). Instead of the rotary filter, it is possible to use a lightsource (e.g., an LED light source) that emits the light having awavelength band for each color.

In the description according to the first embodiment and the secondembodiment described above, the imaging element 242 operates under thecontrol of the control unit 409; however, the illumination controller408 (the phase setting unit 408 a) may be provided at the side of theendoscope 2 so that the strobe emission is controlled at the side of theendoscope 2. In the description, the imaging element 242 operates basedon the clock signal generated by the processing device 4; however, aclock generator may be provided in the endoscope 2 so that the imagingelement 242 operates based on the clock signal generated by the clockgenerator (the clock signal generated by the endoscope 2), or theimaging element 242 may operate based on a clock signal generated by anexternal clock generator.

In the description according to the first embodiment and the secondembodiment described above, the AGC 401 is provided in the processingdevice 4; however, the AGC 401 may be provided in the endoscope 2 (e.g.,the imaging unit 24).

In the description according to the first embodiment and the secondembodiment described above, the object is a vocal cord; however, anyobject other than a vocal cord is applicable as long as the objectvibrates at a high speed and the frequency thereof is detectable by thevocal-cord frequency detecting unit 407.

As described above, the imaging system according to the disclosure isuseful in suppressing the blurring of an image even in the case ofapplication of a rolling shutter method.

According to the disclosure, it is possible to produce an advantage suchthat the blurring of an image may be suppressed even in the case ofapplication of a rolling shutter method.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the disclosure in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. An imaging system comprising: a light sourceconfigured to emit illumination light; an imager configured to store anelectric charge corresponding to an amount of received light and readout the stored electric charge as a signal value by using a rollingshutter method; a frequency detector configured to detect a vibrationalfrequency of a predetermined site of a subject; and an illuminationcontroller configured to control emission of the illumination lightduring a readout period of the signal value, wherein the illuminationcontroller is configured to set a phase for an emission timing of theillumination light in an exposure period during which the imager storesthe electric charge to be an identical phase at the frequency in eachframe, and refer to respective phases set in exposure periods ofchronologically adjacent frames to set an emission timing of theillumination light in the readout period.
 2. The imaging systemaccording to claim 1, wherein the illumination controller is configuredto set a phase for the emission timing of the illumination light in thereadout period to be an average of respective phases set in the exposureperiods of chronologically adjacent frames, and match an emissionintensity of the illumination light in the readout period with anemission intensity of the illumination light in the exposure periodduring which the imager stores the electric charge.
 3. The imagingsystem according to claim 1, wherein the illumination controller isconfigured to set an emission intensity of the illumination light in thereadout period to be lower than an emission intensity of theillumination light in the exposure period during which the imager storesthe electric charge.
 4. The imaging system according to claim 3, whereinthe illumination controller is configured to set a phrase for theemission timing of the illumination light in the readout period to be aphase set in the exposure period of a frame chronologically previous tothe readout period.
 5. The imaging system according to claim 3, whereinthe illumination controller is configured to set a phrase for theemission timing of the illumination light in the readout period to be aphase set in the exposure period of a frame chronologically subsequentto the readout period.
 6. The imaging system according to claim 3,wherein the illumination controller is configured to set a phrase forthe emission timing of the illumination light in the readout period tobe an intermediate phase between phases set in the exposure periods ofchronologically adjacent frames.
 7. The imaging system according toclaim 6, wherein the illumination controller is configured to set thephrase for the emission timing of the illumination light in the readoutperiod to be an average of phases set in the exposure periods ofchronologically adjacent frames.
 8. The imaging system according toclaim 1, further comprising: a vibration receiver configured to receivean input of a vibration of a vocal cord of the subject.
 9. A processingdevice configured to be connected to an endoscope including an imagerconfigured to read out an electric charge stored in a pixel by using arolling shutter method, the processing device comprising: a frequencydetector configured to detect a frequency of a predetermined site of asubject; and an illumination controller configured to control emissionof the illumination light during a readout period of the signal value,wherein the illumination controller is configured to set a phrase for anemission timing of the illumination light in an exposure period duringwhich the imager stores the electric charge to be an identical phase atthe frequency in each exposure period, and refer to respective phasesset in exposure periods of chronologically adjacent frames to set anemission timing of the illumination light in the readout period.
 10. Theprocessing device according to claim 9, wherein the illuminationcontroller is configured to set a phrase for the emission timing of theillumination light in the readout period to be an average of respectivephases set in the exposure periods of chronologically adjacent frames,and match an emission intensity of the illumination light in the readoutperiod with an emission intensity of the illumination light in theexposure period during which the imager stores the electric charge. 11.The processing device according to claim 8, wherein the illuminationcontroller is configured to set a phrase for the emission timing of theillumination light in the exposure period during which the imager storesthe electric charge to be an identical phase at the frequency in eachframe, and set an emission intensity of the illumination light in thereadout period to be lower than an emission intensity of theillumination light in the exposure period during which the imager storesthe electric charge.
 12. The processing device according to claim 11,wherein the illumination controller is configured to set a phrase forthe emission timing of the illumination light in the readout period tobe a phase set in the exposure period of a frame chronologicallyprevious to the readout period.
 13. The processing device according toclaim 11, wherein the illumination controller is configured to set aphrase for the emission timing of the illumination light in the readoutperiod to be a phase set in the exposure period of a framechronologically subsequent to the readout period.
 14. The processingdevice according to claim 11, wherein the illumination controller isconfigured to set a phrase for the emission timing of the illuminationlight in the readout period to be an intermediate phase between phasesset in the exposure periods of chronologically adjacent frames.
 15. Theprocessing device according to claim 14, wherein the illuminationcontroller is configured to set the phrase for the emission timing ofthe illumination light in the readout period to be an average of phasesset in the exposure periods of chronologically adjacent frames.
 16. Theprocessing device according to claim 9, wherein the frequency detectoris configured to detect a frequency of a vocal cord of a subject.
 17. Anillumination control method implemented by an imaging system including:a light source configured to emit illumination light; and an imagerconfigured to store an electric charge corresponding to an amount ofreceived light and read out the stored electric charge as a signal valueby using a rolling shutter method, the illumination control methodcomprising: detecting a vibrational frequency of a predetermined site ofa subject; setting a phrase for an emission timing of the illuminationlight in an exposure period during which the imager stores the electriccharge to be an identical phase at the frequency in each frame; andreferring to respective phases set in exposure periods ofchronologically adjacent frames to set an emission timing of theillumination light in a readout period of the signal value.